Cells

ABSTRACT

There is described a fuel cell or electrolytic cell comprising an ion-conductive polymeric material which includes a first repeat unit of formula (I): —(O-Ph 1 -CO-Ph 1 -O-Ph 1 -CO-Ph 1 )-, and a second repeat unit of formula (II): —(O-Ph 2 -O-Ph 3 -CO-Ph 4 )-, or of formula (III): (O-Ph 2 -O-Ph 3 -SO 2 -Ph 4 )-; wherein Ph 1 , Ph 2 , Ph 3  and Ph 4  independently represent phenyl moieties and wherein said second repeat unit is provided with ion-exchange sites. The polymeric material may include a third repeat unit which is amorphous.

This application is the U.S. National Phase of International ApplicationPCT/GB02/04242, filed 18 Sep. 2002, which designated the U.S.

This invention relates to cells and particularly, although notexclusively, relates to a fuel cell per se and an electrolytic cell perse. Especially preferred embodiments relate to fuel cells.

One type of polymer electrolyte membrane fuel cell (PEMFC), shownschematically in FIG. 1 of the accompanying diagrammatic drawings, maycomprise a thin sheet 2 of a hydrogen-ion conducting Polymer ElectrolyteMembrane (PEM) sandwiched on both sides by a layer 4 of platinumcatalyst and an electrode 6. The layers 2, 4, 6 make up a MembraneElectrode Assembly (MEA) of less than 1 mm thickness.

In a PEMFC, hydrogen is introduced at the anode (fuel electrode) whichresults in the following electrochemical reaction:

-   -   Pt-Anode (Fuel Electrode) 2H₂→4H⁺+4e⁻

The hydrogen ions migrate through the conducting PEM to the cathode.Simultaneously, an oxidant is introduced at the cathode (oxidantelectrode) where the following electrochemical reaction takes place:

-   -   Pt-Cathode (Oxidant Electrode) O₂+4H⁺+4e⁻→2H₂O

Thus, electrons and protons are consumed to produce water and heat.Connecting the two electrodes through an external circuit causes anelectrical current to flow in the circuit and withdraw electrical powerfrom the cell.

Preferred ion-conducting polymeric materials for use as components ofpolymer electrolyte membranes in fuel cells have high conductivity (lowEW, or high ion-exchange capacities) and optimum water uptake for goodconductivity and mechanical properties. To increase conductivity of apolymeric material it may be provided with an increased concentration ofion-exchange sites, for example sulphonate groups. However, the greaterthe ionic character of the polymeric material, the more soluble thepolymeric material is likely to be in water and/or the water absorbanceof the polymeric material may increase too much. Since water at hightemperature is generated as a bi-product of the electrochemical reactionin a fuel cell, the greater the solubility and/or water uptake of thepolymeric material, the greater the rate of disintegration of thepolymeric material and the lower the useful lifetime of the cell.

U.S. Pat. No. 5,362,836 (Hoechst) discloses, in the specific examples,only the preparation of sulphonated polyetheretherketone and sulphonatedpolyetheretheretherketoneketone homopolymers. The sulphonationconditions are varied to vary the level of sulphonation and, therefore,properties of the polymers. No values are given for the boiling wateruptake of the sulphonated polymers prepared. Furthermore, it should beappreciated that it is difficult to precisely control and/or reproducethe level of sulphonation and, consequently, the properties of theion-conductive polymers and that this could lead to difficulties inproducing polymers of the type described for commercial use.

U.S. Pat. No. 5,438,082 (Hoechst), U.S. Pat. No. 5,561,202 (Hoechst) andU.S. Pat. No. 5,741,408 (Hoechst) address the problem of preparingpolymer electrolyte membranes comprising sulphonated aromaticpolyetherketones which have increased stability. The solution describedinvolves the preparation of sulphonated aromatic polyetherketonepolymers, conversion of sulphonate groups of the polymers to sulphonylchloride groups, treatment of the sulphonyl chloride groups with anamine containing at least one cross-linkable substituent to produce asulphonamide group, hydrolysing unreacted sulphonyl chloride groups,isolating the resultant aromatic sulphonamide and dissolving it in anorganic solvent, converting the solution into a film and thencross-linking the crosslinkable substituents in the film.

U.S. Pat. No. 5,795,496 (California Institute of Technology) describespolymer materials for electrolyte membranes in fuel cells which areintended to have high proton conductivity and be stable at hightemperature. Preferred materials are sulphonated polyetheretherketone orsulphonated polyethersulphone. These materials are modified, bycontrolled cross-linking of sulphonate groups, to provide materials withasymmetric permeability properties.

U.S. Pat. No. 5,834,566 (Hoechst) addresses the problem of providingfilms of improved properties for electrochemical uses. The solutiondescribed is the provision of homogenous polymer alloys, for example ofsulphonated polyetherketone and non-sulphonated polyethersulphone, incombination with a hydrophilic polymer, for example ofpolyvinylpyrrolidone or polyglycol dimethylether.

WO96/29360 (Hoechst) addresses the problem of increasing the level ofsulphonation of polyetherketones by providing a method of sulphonating—O-phenyl-CO— units thereof. The specific examples disclose theapplication of the method to polyetheretherketone andpolyetheretherketoneketone homopolymers.

It will be appreciated from the above that there have been many proposedsolutions to the problem of providing suitable ion-conductive polymericmaterials for use in fuel cells and that some of the proposals arecomplex, for example by including multi-step processes, potentiallyexpensive and/or difficult to reproduce on a commercial scale.

It is an object of the present invention to provide an ion-conductivepolymeric material for a fuel cell or electrolytic cell which may beimproved compared to prior art proposals.

The present invention is based on the discovery of certain copolymerswhich are surprisingly advantageously adapted for use in fuel cells orelectrolytic cells.

According to a first aspect of the invention, there is provided a fuelcell or an electrolytic cell comprising an ion-conductive polymericmaterial which includes a first repeat unit of formula—(O-Ph¹—CO-Ph¹-O-Ph¹-CO-Ph¹)-  Iand a second repeat unit of formula—(O-Ph²-O-Ph³-CO-Ph⁴)-  IIor of formula—(O-Ph²-O-Ph³-SO₂-Ph⁴)-  IIIwherein Ph¹, Ph², Ph³ and Ph⁴ independently represent phenyl moietiesand wherein said second repeat unit is provided with ion-exchange sites.

Surprisingly, it is found that ion-conductive polymeric materials of thetype described have boiling water uptakes, when used in fuel cellsand/or electrolytic cells, which are much lower than expected and, moreparticularly, much lower than found for ion-conductive polymericmaterials of similar equivalent weights (EW) comprising a singleion-conducting homopolymer of formula I, II or III.

Unless otherwise stated in this specification, a phenyl moiety may have1,4- or 1,3-, especially 1,4-, linkages to moieties to which it isbonded.

Said ion-conductive polymeric material is preferably crystalline.

The existence and/or extent of crystallinity in a polymer is preferablymeasured by wide angle X-ray diffraction, for example as described byBlundell and Osborn (Polymer 24, 953, 1983). Alternatively, DifferentialScanning Calorimetry (DSC) could be used to assess crystallinity. Thelevel of crystallinity in said ion-conductive polymeric material may beat least 0.5% suitably at least 1%, preferably at least 5%, morepreferably at least 10%, especially at least 15% weight fraction,suitably when measured as described by Blundell and Osborn. In somecases, the level of crystallinity, when measured as described may be atleast 20% weight fraction. The level of crystallinity in said firstpolymeric material may be less than 30% weight fraction, preferably lessthan 25% weight fraction.

Said ion-conductive polymeric material suitably includes a repeat unitwhich is crystalline and a repeat unit which is amorphous. Said firstrepeat unit is preferably crystalline. Preferably, less than 1 mole % ofgroups Ph¹ in said polymeric material are sulphonated and/or otherwisefunctionalised. Preferably, said first repeat unit comprisesunsubstituted phenyl groups Ph¹ with said groups Ph¹ suitably having1,4-linkages to the —O— and —CO— groups to which they are bonded.Preferably, substantially no groups Ph¹ are substituted in saidion-conductive polymeric material.

Said second repeat unit preferably includes ion-exchange sites.Suitably, to provide said ion-exchange sites, said second repeat unit issulphonated, phosphorylated, carboxylated, quaternary-aminoalkylated orchloromethylated, and optionally further modified to yield —CH₂PO₃H₂,—CH₂NR₃ ²⁰⁺ where R²⁰ is an alkyl, or —CH₂NAr₃ ^(x+) where Ar^(x) is anaromatic (arene), or provided with —OSO₃H or —OPO₃H₂ cationic exchangesites as described in WO95/08581.

Preferably, said second repeat unit is sulphonated. Preferably, the onlyion-exchange sites of said second repeat unit are sites which aresulphonated.

References to sulphonation include a reference to substitution with agroup —SO₃M wherein M stands for one or more elements selected with dueconsideration to ionic valencies from the following group: H, NR₄ ^(y+),in which R^(y) stands for H, C₁-C₄ alkyl, or an alkali or alkaline earthmetal or a metal of sub-group 8, preferably H, NR₄ ⁺, Na, K, Ca, Mg, Fe,and Pt. Preferably M represents H.

Preferably less than 1 mole % of groups Ph³ in said second unit aresulphonated and/or otherwise functionalised. Preferably less than 1 mole% of groups Ph⁴ are sulphonated and/or otherwise functionalised.Preferably, substantially no groups Ph³ are substituted. Preferably,substantially no groups Ph⁴ are substituted. Preferably Ph³ representsan unsubstituted phenyl group, suitably having 1,4-linkages to the —O—and —CO— (or —SO₂—) groups to which it is bonded. Preferably, Ph⁴represents an unsubstituted phenyl groups, suitably having 1,4-linkagesto the —O— and —CO— (or —SO₂—) groups to which it is bonded.

Suitably, greater than 70 mole %, preferably greater than 80 mole %,more preferably greater than 90 mole % of groups Ph² in said second unitare provided with ion-exchange sites, especially sulphonate groups.Groups Ph² may be provided with a single ion-exchange site—i.e. they arepreferably only monosulphonated.

In general terms, phenyl groups of —O-phenyl-O— moieties (e.g. Ph²) maybe provided with ion-exchange sites, for example sulphonated, readily,e.g. using the relatively mild method described in Examples 2a to 2chereinafter, (i.e. using a sulphuric acid concentration of less than98.5% and avoiding the use of oleum) so that up to 100 mole % of thephenyl groups are provided with ion-exchange sites (e.g. sulphonated).However, the phenyl groups of —O-phenyl-CO— moieties and of—O-phenyl-SO₂— moieties (e.g. Ph¹, Ph³ and Ph⁴) are relatively difficultto provide with ion-exchange sites (and, therefore, are not providedwith ion-exchange sites) due to deactivation of the phenyl moieties by—CO— or —SO₂— groups.

Preferably, Ph² represents a phenyl group provided with an ion-exchangesite wherein the phenyl group has 1,4-linkages to the —O— groups towhich it is bonded.

Said second unit suitably is, by virtue of it being provided withion-exchange sites, amorphous.

Said ion-conductive polymeric material could include repeat units offormula II and III, each of which is provided with ion-exchange sites.Preferably, however, it includes either unit II or unit III (and notboth).

An especially preferred second repeat unit is of formula II. Thus, saidsecond repeat unit is preferably an-ether-(monosulphonated)phenyl-ether-(unsubstituted)phenyl-carbonyl-(unsubstituted)phenyl-unit.

Suitably, “a” represents the mole % of units of formula I in saidion-conductive polymeric material, and “b” represents the sum of themole % of units of formulae II and III in said polymeric material.Suitably, the ratio of “a” to “b” in said polymeric material is lessthan 4, preferably less than 3, more preferably less than 2, especiallyless than 1. The ratio of “a” to “b” may be at least 0.15, suitably atleast 0.25, preferably at least 0.3, more preferably at least 0.4,especially at least 0.5.

Said ion-conductive polymeric material may be a random or blockcopolymer comprising units I, II and/or III. Preferably, saidion-conductive polymeric material is a random copolymer.

Said ion-conductive polymeric material may include a third repeat unitwhich is suitably different from units I, II and III. Said third unit ispreferably amorphous. Said third unit is preferably not crystalline orcrystallisable. Said third unit is preferably not provided withion-exchange sites. Said optional third unit preferably includes phenylgroups linked by —CO—, —SO₂—, —O— and/or —S— provided said third unit ismore difficult to provide with ion-exchange sites (e.g. sulphonate)compared to the ease with which said second unit (prior to itsfunctionalisation as described) can be provided with ion-exchange sites(e.g. sulphonated) and provided said third unit is amorphous. To thisend, said third unit suitably includes a means to render it amorphous(hereinafter “said amorphous means”) and/or not crystallisable withpolyetherketone units. Said third unit may include a moiety of formula-Q-Z-Q- wherein Z represents an aromatic group containing moiety and Qis —O— or —S—, wherein said unit of formula -Q-Z-Q- is not symmetricalabout an imaginary line which passes through the two -Q- moietiesprovided, however, that said unit is not derived fromdihydroxybenzophenone substituted by groups Q at the 4- and 4′-positions(since such a benzophenone acts in the manner of a symmetrical moiety byvirtue of the carbonyl group being substantially similar to an ethergroup thereby allowing the carbonyl group to be interchanged with anether group in a polyaryletherketone crystal lattice).

Examples of units of formula -Q-Z-Q- (especially where Q is —O—) are asfollows:

Said third repeat unit preferably includes at least one of thefollowing: a sulphone moiety in the polymer backbone; a1,3-disubstituted phenyl moiety in the polymer backbone; or a functionalgroup pendent from a phenyl moiety in the polymer backbone.

Preferred optional third units are of general formula—O-Ph-(SO₂-Ph)_(n1)-(CO-Ph)_(n2)-[AMOR]-  IVwherein Ph represents a phenyl group, n1 is 0, 1 or 2, n2 is 0, 1 or 2and AMOR represents an amorphous unit, for example of formulae:

The phenyl groups of the third unit of formula IV may be 1,3- or1,4-substituted by the groups shown. Preferably, they are1,4-substituted.

Preferred third units are: -ether-phenyl-ketone-phenyl-[AMOR]- (i.e.n1=0, n2=1), -ether-phenyl-sulphone-phenyl-[AMOR]- (i.e. n1=1, n2=0),where [AMOR] represents V, VI or VII.

Preferably, “c” represents the mole % of said third units in saidion-conductive polymeric material and “a” and “b” are as describedabove. The ratio of “c” to the sum of “a” and “b” is suitably less than0.25, preferably less than 0.2, more preferably less than 0.15,especially less than 0.125.

Suitably, “c” is 30 mole % or less, preferably 20 mole % or less, morepreferably 15 mole % or less, especially 10 mole % or less. Suitably “a”is at least 30 mole %, preferably at least 40 mole %, more preferably atleast 45 mole %, especially at least 50 mole %. Suitably, “a” is 85 mole% or less. Suitably, “b” is at least 70 mole % or less, preferably 60mole % or less, more preferably 55 mole % or less, especially 50 mole %or less.

The equivalent weight (EW) of said ion-conductive polymeric material ispreferably less than 850 g/mol, more preferably less than 800 g/mol,especially less than 750 g/mol. The EW may be greater than 300, 400 or500 g/mol.

The boiling water uptake of ion-conductive polymeric material measuredas described in Example 4 is suitably less than 350%, preferably lessthan 300%, more preferably less than 250%.

The glass transition temperature (T_(g)) of said ion-conductivepolymeric material may be at least 144° C., suitably at least 150° C.,preferably at least 154° C., more preferably at least 160° C.,especially at least 164° C. In some cases, the Tg may be at least 170°C., or at least 190° C. or greater than 250° C. or even 300° C.

Said ion-conductive polymeric material may have an inherent viscosity(IV) of at least 0.1, suitably at least 0.3, preferably at least 0.4,more preferably at least 0.6, especially at least 0.7 (which correspondsto a reduced viscosity (RV) of least 0.8) wherein RV is measured at 25°C. on a solution of the polymer in concentrated sulphuric acid ofdensity 1.84 gcm⁻³, said solution containing 0.1 g of polymer per 100cm⁻³ of solution. IV is measured at 25° C. on a solution of polymer inconcentrated sulphuric acid of density 1.84 gcm³, said solutioncontaining 0.1 g of polymer per 100 cm³ of solution. The measurements ofboth RV and IV both suitably employ a viscometer having a solvent flowtime of approximately 2 minutes.

The main peak of the melting endotherm (Tm) for said ion-conductivepolymeric material may be at least 300° C.

Said semi-crystalline polymer may comprise a film, suitably having athickness of less than 1 mm, preferably less than 0.5 mm, morepreferably less than 0.1 mm, especially less than 0.05 mm. The film mayhave a thickness of at least 5 μm.

The invention of the first aspect preferably relates to a fuel cell.Said ion-conductive polymeric material preferably comprises a part of anion-conducting membrane of said fuel cell. Said ion-conducting membraneis preferably substantially non-permeable. Said ion-conductive membranemay consist essentially of said ion-conductive polymeric material. Inthis case, said membrane comprises a unitary material which may define aPEM of the fuel cell. A catalyst material may be associated with thepolymeric material, suitably on opposite sides thereof. Alternatively,said ion-conductive polymeric material may be part of a compositeion-conducting membrane. Said composite ion-conducting membrane maycomprise said ion-conductive polymeric material blended with otherion-conducting or non-ion-conducting amorphous or crystalline polymericmaterials. Alternatively, said ion-conductive polymeric material may beassociated with a composite membrane material. For example, saidion-conductive polymeric material in the form of an unsupportedconductive polymer film can be contacted with, for example laminated to,a said composite membrane material. Alternatively, one of either saidcomposite membrane material or said ion-conductive polymeric materialmay be impregnated with the other one of either said composite membranematerial or said ion-conductive polymeric material.

Said composite membrane material may be a support material forsupporting said ion-conductive polymeric material. In this case, saidcomposite membrane material preferably is stronger and/or has a lowerwater absorbance compared to said ion-conductive polymeric material.

Alternatively, said ion-conductive polymeric material may be a supportfor the composite membrane material.

The invention extends to a plurality of fuel cells as describedaccording to the first aspect. The fuel cells are preferablysubstantially identical to one another and are preferably provided in astack in series. Greater than 50 or even greater than 100 of said fuelcells may be provided in a said stack.

Said plurality of fuel cells may together include more than 0.1 m²,suitably more than 0.5 m², preferably more than 1 m², more preferablymore than 5 m² of said ion-conductive polymeric material. The amount ofsaid ion-conductive polymeric material may be less than 100 m².

According to a second aspect of the invention, there is provided apolymer electrolyte membrane for a fuel cell or electrolytic cell(especially for a fuel cell), the membrane comprising an ion-conductivepolymeric material as described according to said first aspect.

Said polymer electrolyte membrane (PEM) may have a dimension in a firstdirection of at least 1 cm. The dimension of the PEM in a seconddirection, perpendicular to the first direction, may also be at least 1cm. Where the PEM is circular, the diameter may be at least 1 cm. Insome cases, for example for vehicle applications, the dimension(s) inthe first and/or second direction(s) may be at least 10 cm or at least20 cm. The dimension(s) in the first and second direction(s) is/aresuitably less than 100 cm, preferably less than 50 cm, more preferablyless than 35 cm.

Said PEM may comprise one or more layers wherein, suitably, at least onelayer comprises a film of said semi-crystalline polymer. Said membranemay have a thickness of at least 5 μm and, suitably, less than 1 mm,preferably less than 0.5 mm, more preferably less than 0.1 mm,especially less than 0.05 mm.

According to a third aspect of the invention, there is provided amembrane electrode assembly for a fuel cell which comprises anion-conductive polymeric material according to said first aspectassociated with a catalyst material. Catalyst material is preferablyassociated with opposing sides of the ion-conducting polymeric material.

According to a fourth aspect of the present invention, there is provideda method of making a fuel cell or electrolytic cell, the methodcomprising incorporating an ion-conductive polymeric material accordingto said first aspect into said fuel cell or electrolytic cell.

According to a fifth aspect of the invention, there is provided a methodof making a fuel cell or electrolytic cell, the method comprisingincorporating, into the fuel cell or electrolytic cell, anion-conductive polymeric material prepared by:

-   -   (A) polycondensing 4,4′-dihydroxybenzophenone (DHB),        4,4′-difluorobenzophenone (BDF) and hydroquinone (HQ);    -   (B) treating the polymeric material formed with a means for        providing said ion-exchange sites.

The polycondensation reaction may, optionally, be carried out in thepresence of other monomers. Examples include4,4′-dichlorodiphenylsulphone (DCDPS) and/or4,4′-difluorodiphenylsulphone (DFDPS).

The polycondensation reaction described for making an ion-conductivepolymeric material according to the first aspect and/or using the methoddescribed in the fifth aspect is suitably carried out in the presence ofa base, especially an alkali metal carbonate or bicarbonate or a mixtureof such bases. Preferred bases for use in the reaction include sodiumcarbonate and potassium carbonate and mixtures of these.

The identity and/or properties of the polymers prepared in apolycondensation reaction described may be varied according to thereaction profile, the identity of the base used, the temperature of thepolymerisation, the solvent(s) used and the time of the polymerisation.Also, the molecular weight of a polymer prepared may be controlled byusing an excess of halogen or hydroxy reactants, the excess being, forexample, in the range 0.1 to 5.0 mole %

Said means for providing said ion-exchange sites preferably involvessulphonating the polymeric material. Sulphonation conditions arepreferably selected wherein Ph² phenyl groups can be sulphonated butrelatively deactivated Ph¹, Ph³ and Ph⁴ phenyl groups generally cannotbe sulphonated. To this end, sulphonation may be carried out inconcentrated sulphuric acid (suitably at least 96% w/w, preferably atleast 97% w/w, more preferably at least 98% w/w; and preferably lessthan 98.5% w/w) at an elevated temperature. For example, dried polymermay be contacted with sulphuric acid and heated with stirring at atemperature of greater than 40° C., preferably greater than 55° C., forat least one hour, preferably at least two hours, more preferably atleast five hours especially at least ten hours. The desired product maybe caused to precipitate, suitably by contact with cooled water, andisolated by standard techniques. Advantageously, the method can be usedto sulphonate 100 mole % of Ph² phenyl groups and once this level ofsulphonation has been effected no further sulphonation occurs. Thus,there is no need to precisely control the sulphonation conditions (e.g.reaction time) beyond ensuring that the reaction has proceeded longenough to substantially fully mono-sulphonate the Ph² phenyl groups.This facilitates the preparation of batches of substantially identicalion-conductive polymeric materials and contrasts with processes whichneed to be stopped when a desired level of sulphonation has beenachieved, for example where more vigorous conditions are used tosulphonate —O-phenyl-CO— groups in polymeric materials.

When said ion-conducting polymeric material includes a third unit whichis amorphous and not provided with ion-exchange sites, thepolycondensation reaction may be carried out in the presence of one ormore other monomers. Preferred examples of such other monomers are Bis-Sand 2,4-DHB. Other examples are1,3-bis(4-fluorobenzoyl)benzene(1,3-DKDF) and its sulphone analogue.

Preferred combinations of monomers which after polycondensation andtreatment to provide ion-exchange sites (e.g. after sulphonation) may beof utility in fuel cells as described are detailed in the Table belowwherein the * in each row indicates the monomers which can be used toprepare preferred polymers. The following abbreviations are used in thetable:

Sulphone Sulphone analogue analogue 2,4- 1,3- of 1,4- of 1,3- BDF DHB HQDCDPS/DFDPS Bis-S DHB DKDF DKDFDKDF * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *BDF 4,4′-difluorobenzophenone HQ hydroquinone DHB4,4′-dihydroxybenzophenone Bis-S 4,4′-dihydroxydiphenylsulphone DCDPS4,4′-dichlorodiphenylsulphone DFDPS 4,4′-difluorodiphenylsulphone2,4-DHB 2,4-dihydroxybenzophenone 1,3-DKDF1,3-bis-(4-fluorobenzoyl)benzene

According to a sixth aspect of the invention, there is provided a methodof making a polymer electrolyte membrane of a fuel cell or electrolyticcell (especially of a fuel cell), the method including providing anion-conductive polymeric material as described herein in solution,forming said solution into a desired form (e.g. casting the solution toform a membrane) and providing conditions for removal of the solvent ofsaid solution.

According to a seventh aspect of the invention, there is provided amethod of making a membrane electrode assembly of a fuel cell, themethod comprising associating a catalyst material with an ion-conductivepolymeric material as described herein.

Any feature of any aspect of any invention or embodiment describedherein may be combined with any feature of any aspect of any otherinvention or embodiment described herein mutatus mutandis.

Specific embodiments of the invention will now be described by way ofexample.

In the following examples, abbreviations used are as hereinbeforedescribed.

The following products are referred to hereinafter:

-   -   PEEK™450P (Trade Mark)—polyetheretherketone obtained from        Victrex Plc of Thornton Cleveleys, UK.    -   PEK™P22 (Trade Mark)—polyetherketone also obtained from Victrex        Plc.

Unless otherwise stated, all chemicals referred to hereinafter were usedas received from Sigma-Aldrich Chemical Company, Dorset, U.K. 1,3-DKDFcan be made as described in Polymer 29, 358 (1988).

EXAMPLE 1a

A 700 ml flanged flask fitted with a ground glass Quickfit lid,stirrer/stirrer guide, nitrogen inlet and outlet was charged with4,4′-difluorobenzophenone (88.85 g, 0.4072 mole) (BDF), hydroquinone(24.22 g, 0.22 mole) (HQ), 4,4′-dihydroxybenzophenone 38.56 g, 0.18mole) (DHB) and diphenysulphone (320 g) and purged with nitrogen forover 1 hour. The contents were then heated under a nitrogen blanket tobetween 140 and 150° C. to form an almost colourless solution. Whilemaintaining a nitrogen blanket, dried sodium carbonate (42.39 g, 0.4mole) and potassium carbonate (1.10 g, 0.008 mole) were added. Thetemperature was raised gradually to 330° C. over 3 hours then maintainedfor 20 minutes.

The reaction mixture was allowed to cool, milled and washed with acetoneand water. The resulting polymer was dried in an air oven at 120° C. Thepolymer had a melt viscosity at 400° C., 1000 sec⁻¹ of 0.46 kNsm⁻².

EXAMPLE 1b

A 700 ml flanged flask fitted with a ground glass Quickfit lid,stirrer/stirrer guide, nitrogen inlet and outlet was charged with4,4′-difluorobenzophenone (88.85 g, 0.4072 mole), hydroquinone (24.22 g,0.22 mole), 4,4′-dihydroxybenzophenone (34.32 g, 0.160 mole),4,4′-dihydroxydiphenylsulphone (5.0 g, 0.02 mole), and diphenysulphone(320 g) and purged with nitrogen for over 1 hour. The contents were thenheated under a nitrogen blanket to between 140 and 150° C. to form analmost colourless solution. While maintaining a nitrogen blanket, driedsodium carbonate (43.24 g, 0.408 mole) was added. The temperature wasraised gradually to 330° C. over 3 hours then maintained for 50 minutes.

The reaction mixture was allowed to cool, milled and washed with acetoneand water. The resulting polymer was dried in an air oven at 120° C. Thepolymer had a melt viscosity at 400° C., 1000 sec⁻¹ of 0.34 kNsm⁻².

EXAMPLES 1c-1e

The polymerisation procedure of Example 1b was followed, for 1c-1e,except that copolymer was prepared by varying the mole ratios of thehydroxy-containing reactants and by omission of the potassium carbonate.

A summary of the mole ratios and MVs are detailed in Table 1 below.

TABLE 1 Polymer Composition (mole ratio) MV Example BDF HQ DHB Bis-S(kNsm⁻²) 1a 1.02 0.55 0.45 — 0.46 1b 1.02 0.55 0.40 0.05 0.34 1c 1.020.55 0.36 0.09 0.55 1d 1.02 0.58 0.42 — 0.32 1e 1.02 0.65 0.35 — 0.34

EXAMPLES 2a -2e Sulphonation of Polymers Examples 1a-1e

The polymers from Examples 1a-1e were sulphonated by stirring therespective polymers in 98% sulphuric acid (7.0 g polymer/100 g sulphuricacid) for >21 hours at 65° C. Thereafter, the reaction solution wasallowed to drip into stirred deionised water. Sulphonated polymer wasprecipitated as free-flowing beads. Recovery was by filtration, followedby washing with deionised water until the pH was neutral and subsequentdrying. In general, titration confirmed that 100 mole % of the phenylgroups present as ether-phenyl-ether para linkages had sulphonated,giving one sulphonic acid group, ortho to the ether linkage, on each ofthe aromatic rings. The phenyl groups present in ether-phenyl-ketonemoieties were unsulphonated as were the phenyl groups present inether-phenyl-ketone-phenyl-ether-sulphones moieties (if present).

EXAMPLES 2f Sulphonation of Polyetheretherketone (Comparative)

A 500 ml, 3-necked, round-bottomed flask fitted with a stirrer/stirrerguide, nitrogen inlet and outlet and a thermometer was charged with 98%sulphuric acid (180 g). The sulphuric acid was heated under a blanket ofnitrogen to 50° C. While maintaining a nitrogen blanket and stirringpolyetheretherketone (PEEK™ 450P, Victrex plc) was added. The polymerdissolved and was stirred at 50° C. for 90 minutes. The solution wasquickly cooled to 20° C., thereafter allowed to drip into stirreddeionised water. Sulphonated polymer precipitated as free-flowing beads.Recovery was by filtration, followed by washing with deionised wateruntil the pH was neutral and subsequent drying. By titration theEquivalent Weight was 644. It should be appreciated that the EW dependson the duration and temperature of the sulphonation reaction—the greaterthe duration and temperature, the more sulphonated the polymer.

EXAMPLES 2g Sulphonation of Polyetherketone (Comparative)

A 500 ml, 3-necked, round-bottomed flask fitted with a stirrer/stirrerguide, nitrogen inlet and outlet and a thermometer was charged with 98%sulphuric acid (180 g) and, while stirring, polyetherketone (PEK™ P22,Victrex plc) (20 g) was added. The temperature was increased to 55° C.and oleum (20% free SO₃) (120 g) was added. The solution was stirred for60 minutes at 35° C. The solution was quickly cooled to 20° C.,thereafter, allowed to drip into stirred deionised water. Sulphonatedpolymer precipitated as free-flowing beads. Recovery was by filtration,followed by washing with deionised water until the pH was neutral andsubsequent drying. By titration the Equivalent Weight was 667. As forExample 2f, the greater the duration and temperature of the sulphonationreaction, the more sulphonated the polymer.

EXAMPLES 3a-3g Membrane Fabrication

Membranes were produced from the sulphonated polymers of respectiveExamples 2a-2g by dissolving respective polymers in N-methylpyrrolidone(NMP). The polymers were dissolved at 80° C. at their maximumconcentration. The homogeneous solutions were cast onto clean glassplates and then drawn down to give 400 micron films, using a stainlesssteel Gardner Knife. Evaporation at 100° C. under vacuum for 24 hoursproduced membranes of mean thickness 40 microns.

EXAMPLES 4a-4g Water-Uptake of the Membranes

5 cm×5 cm×40 microns sample of the membranes from Examples 3a-3g wereimmersed in boiling deionised water (500 ml) for 60 mins, removed anddried quickly with lint-free paper to remove surface water, weighed,dried in an oven at 50° C. for 1 day, allowed to cool to ambienttemperature in a desiccator then weighed quickly. The % water-uptake wascalculated as follows and the results are provided in Table 2.

${\%\mspace{14mu}{Water}\text{-}{uptake}} = {\frac{{{Wet}\mspace{14mu}{Weight}} - {{Dry}\mspace{14mu}{Weight}}}{{Dry}\mspace{14mu}{Weight}} \times 100}$

TABLE 2 Boiling water Sulphonated uptake as Actual polymer fromdescribed in Theoretical EW (by Example No. Example 4 (%) EW titration)3a  59 690 700 3b  93 692 667 3c 135 695 733 3d 106 645 641 3e 234 579590 3f (comp) Broke up — 644 3g (comp) 370 — 670

Referring to Table 2, it should be noted that the sulphonatedpolyetherketone polymer (Example 3g) had a substantially higher boilingwater uptake compared to the copolymers of Examples 3a to 3e forcomparable EW. In the case of sulphonated polyetherethereketone (Example3f) the boiling water uptake was so high that the polymeric materialbroke up. It is highly surprising that whereas respective homopolymersof sulphonated polyetheretherketone and sulphonated polyetherketone havevery high boiling water uptakes, copolymers comprising sulphonatedpolyetherethereketone with polyetherketone have significantly lowerboiling water uptakes for similar EWs.

EXAMPLE 5 Post Treatment of the Membranes of Examples 4a, 4c and 4e withAcetone

The 5 cm×5 cm×40 microns sample of membrane from Examples 4a, 4c and 4ewere immersed in refluxing acetone (100 ml) for 60 mins, removed anddried in an oven at 50° C. for 1 day, immersed in boiling deionisedwater (500 ml) for 60 mins, removed and dried quickly with lint-freepaper to remove surface water, weighed, dried in an oven at 50° C. for 1day, allowed to cool to ambient temperature in a desiccator then weighedquickly. The % water-uptake was calculated as described previously andsummarised in Table 3.

TABLE 3 Boiling water Boiling water uptake after Sulphonated uptake asacetone treatment polymer from described in as described in Example No.Example 4 (%) Example 5 (%) 3a 59 61 3c 135 84 3e 234 100

The acetone treatment can increase crystallinity of crystallinepolyaryletherketones. Table 3 shows that a substantial reduction inboiling water uptake can be achieved in some circumstances (Examples 3cand 3e). In some cases, where crystallinity of the polymer is alreadyhigh, the acetone treatment cannot effect an increase (Example 3a).

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings), may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extend to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

1. A fuel cell or an electrolytic cell comprising an ion-conductivepolymeric material which includes a first repeat unit of formula:—(O-Ph¹-CO-Ph¹-O-Ph¹-CO-Ph¹)-  I and a second repeat unit of formula—(O-Ph³-O-Ph³-CO-Ph⁴)-  II or of formula—(O-Ph²-O-Ph³-SO₂-Ph⁴)-  III wherein Ph¹, Ph², Ph³ and Ph⁴ independentlyrepresent phenyl moieties and wherein said second repeat unit isprovided with ion-exchange sites.
 2. A cell according to claim 1,wherein said ion-conductive polymeric material is crystalline.
 3. A cellaccording to claim 1, wherein said ion-conductive polymeric materialincludes a repeat unit which is crystalline and a repeat unit which isamorphous.
 4. A cell according to claim 1, wherein said first repeatunit is crystalline.
 5. A cell according to claim 1, wherein said firstrepeat unit comprises unsubstituted phenyl groups Ph¹ with said groupsPh¹ having 1,4-linkages to the —O— and —CO— groups to which they arebonded.
 6. A cell according to claim 4, wherein said second repeat unitincludes ion-exchange sites.
 7. A cell according to claim 6, whereinsaid second repeat unit is sulphonated.
 8. A cell according to claim 1,wherein Ph³ represents an unsubstituted phenyl group having 1,4-linkagesto the —O— and —CO— or —SO₂— groups to which it is bonded.
 9. A cellaccording to claim 8, wherein Ph⁴ represents an unsubstituted phenylgroup having 1,4-linkages to the —O— and —CO— or —SO₂— groups to whichit is bonded.
 10. A cell according to claim 9, wherein Ph² represents aphenyl group provided with an ion-exchange site wherein the phenyl grouphas 1,4-linkages to the —O— groups to which it is bonded.
 11. A cellaccording to claim 1, wherein less than 1 mole % of groups Ph¹ in saidpolymeric material are functionalised; less than 1 mole of groups Ph³ insaid second unit are functionalised; less than 1 mole % of groups Ph⁴are functionalised; and greater than 70 mole % of groups Ph² in saidsecond unit are provided with ion-exchange sites.
 12. A cell accordingto claim 1, wherein said second repeat unit is an-ether-(monosulphonated)phenyl-ether-(unsubstituted)phenyl-carbonyl-unsubstituted)phenyl- unit.
 13. A cellaccording to claim 1, wherein the ratio of mole % of units of formula Iin said ion-conductive polymeric material to the sum of the mole % ofunits of formula II and III in said polymeric material is less than 4but is at least 0.15.
 14. A cell according to claim 1, wherein saidion-conductive polymeric material includes a third repeat unit which isdifferent from units II and III, wherein said third unit is amorphous.15. A cell according to claim 14 which includes at least one of thefollowing: a sulphone moiety in the polymer backbone; a1,3-disubstituted phenyl moiety in the polymer backbone; or a functionalgroup pendent from a phenyl moiety in the polymer backbone.
 16. A cellaccording to claim 1, wherein the equivalent weight (EW) of saidion-conductive polymeric material is less than 850 g/mol and is greaterthan 300 g/mol.
 17. A polymer electrolyte membrane for a fuel cell orelectrolytic cell, the membrane comprising an ion-conductive polymericmaterial according to claim
 1. 18. A membrane electrode assembly for afuel cell which comprises an ion-conductive polymeric material asdescribed in claim 1 associated with a catalyst material.
 19. A methodof making a fuel cell or electrolytic cell, the method comprisingincorporating an ion-conductive polymeric material as described in claim1 into said fuel cell or electrolytic cell.